CN108883505B

CN108883505B - Preparation of composite rods

Info

Publication number: CN108883505B
Application number: CN201680078240.0A
Authority: CN
Inventors: 马克·拉塞尔
Original assignee: Cutting and Wear Resistant Developments Ltd
Current assignee: Cutting and Wear Resistant Developments Ltd
Priority date: 2015-11-09
Filing date: 2016-11-09
Publication date: 2022-04-19
Anticipated expiration: 2036-11-09
Also published as: GB201519765D0; EP3374121B1; GB2545886B; US20200246909A1; US20220176487A1; EP3374121A1; CN108883505A; WO2017081460A1; CA3004202A1; GB2545886A; US11292080B2

Abstract

Preparing the composite material rod. The present invention relates to a method of manufacturing a composite rod from a brazing material and a sheet comprising a cermet. The method includes scoring a surface of the sheet to create at least one localized stress line and subsequently fracturing the sheet along the localized stress line to create a plurality of cermet blocks. Cermet blocks may be combined with brazing material to produce composite rods. In certain embodiments, the sheet may be a cermet cutting blade used.

Description

Preparation of composite rods

Technical Field

The present invention relates to composite rods for hard surfaces of tools, including but not limited to downhole tools for the oil and gas drilling industry.

Background

It is well known to hard face tools by applying a hard coating on the surface of the tool which is intended to withstand abrasive surfaces such as geological formations or to cut hard materials such as metal. This improves the service life of the tool. Coatings for hardfacing typically comprise a mass of a hard cermet material such as tungsten carbide (WC), titanium carbide (TiC) or polycrystalline diamond (PCD) and a braze material wetting the hard material and the surface to be hardfaced, thereby adhering the hard material to the surface.

One particularly cost effective method of hardfacing involves the use of composite rods having cermet blocks embedded within a matrix of brazing material. Such a composite rod may be placed over the surface to be hardfaced and heated above the melting temperature of the braze material (e.g., using an oxyacetylene torch) to cause the braze material and cermet block to flow onto the surface before the braze material resolidifies.

It is desirable to regularly size the hard material blocks. For some applications it is also desirable that they have sharp edges and therefore the hard facing has abrasive properties. This may be useful, for example, for milling tools that cut the metal casing of a wellbore in downhole applications. For other applications, the blocks may be more rounded and smaller in shape to make the hardfaced surface simple and more wear resistant. Wear resistant surfaces are used in downhole drilling equipment and agricultural equipment, such as plow shears (plough shears), i.e. components that are integrated with geological formations.

Composite rods with preformed tetrahedral tungsten carbide blocks are available from Cutting & Wear Resistant Developments Ltd under the trade name Sharkstooth. However, the requirement for preformed WC blocks makes these rods relatively expensive to produce. Composite rods are also manufactured using tungsten carbide blocks removed from waste machined tool bits and the like. These lumps are achieved by crushing the cutter head in a mechanical crusher and then sieving the product to obtain approximately the same size fraction. However, this process results in a waste of about 70% of the raw product, as many are crushed into small pieces that cannot be used.

The present invention seeks to at least partially alleviate the problems of the prior art.

Disclosure of Invention

According to the present invention there is provided a method of manufacturing a composite rod from a brazing material and a sheet comprising a cermet, the method comprising:

scoring the surface of the cermet piece to generate at least one local stress line;

breaking the sheet along local stress lines, thereby creating a plurality of cermet blocks; and

a cermet block is combined with a brazing material to produce a composite rod. This aspect provides a convenient method for breaking up the cermet plate into blocks of a predetermined size and shape with little waste.

In another aspect, the present invention provides a method for hardening a surface to be hardened using a sheet comprising a cermet, the method comprising:

scoring a surface of the sheet to create at least one localized line of stress; breaking the sheet along local stress lines, thereby creating a plurality of cermet blocks; and

a cermet block is brazed to the surface to be hardfaced. Alternatively, the cermet block may be spot welded to the surface to be hardfaced prior to brazing the cermet block to the surface to be hardfaced.

In one embodiment, the act of scoring the surface causes at least a portion of the sheet to crack and eventually break without the application of further external force. This embodiment provides for rapid fracture of the cermet piece into a cermet piece.

In some embodiments, at least a portion of the sheet is broken along the localized stress lines by application of an external force. Scoring the sheet and subsequently applying an external force can contribute to predictable breakage of the sheet. Optionally, the external force comprises the action of a mechanical crusher or press. The mechanical crusher or press may be a hydraulic or pneumatic press with a chisel attached thereto. This allows the press to apply force along the axis of the cutting tips that are desired to break. By providing said local stress lines on the component, even if it does not break directly therefrom, the sheet breaks not only but also along the local stress lines upon application of a relatively small force. Thus, little force is required, saving energy used to operate the crusher, and less sheet breakage occurs along lines other than the local stress lines, thereby reducing waste of raw material.

In another embodiment, thermal stress is generated in the cermet sheet, thereby at least assisting in breaking the sheet along local stress lines. Optionally, the thermal stress is generated by a laser.

In one embodiment, the cermet comprises tungsten carbide.

In another embodiment, the cermet comprises titanium carbide.

Optionally, the cermet-containing material further comprises a superhard material on the surface of the cermet. Such superhard materials may provide particularly good wear and erosion resistance. Further optionally, the superhard material comprises polycrystalline diamond (PCD) or Cubic Boron Nitride (CBN).

In one embodiment, scoring the sheet is accomplished by a first laser. Alternatively, the first laser may be a CO₂A laser or a diode laser.

In one embodiment, the thermal stress is generated at least in part by a second laser different from the first laser. This embodiment may increase the likelihood that the cermet plate will break without the application of external forces. Furthermore, the first and second lasers may be applied simultaneously, thereby reducing the time required to fracture the cermet plate into a plurality of cermet blocks.

In one embodiment, the power of the first laser is between 1 and 3 kW. Preferably, the power of the first laser is between 1.9 and 2.5 kW. Scoring may be performed at a speed between 10 and 30 mm/s. Preferably, scoring is performed at a speed of between 10 and 20mm/s or between 15 and 25 mm/s. Optionally, the spot width of the laser is between 0.1mm and 0.6mm

In one embodiment, scoring the cermet plate is accomplished by loading the sheet onto a table of a laser apparatus, directing a laser onto the table, and moving the table relative to the laser.

Optionally, the cermet wafer comprises used machined tool bits.

According to another aspect of the present invention there is provided a composite rod made according to the above method, wherein the composite rod comprises a cermet block having a score line along at least one edge thereof. Optionally, the score line comprises a residue of a laser score line. The remnants of the laser score line may include areas along the edge of the block that have melted and re-solidified.

Drawings

Embodiments of the present invention are further described below, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a cutting blade for use in a method of making a composite rod in one embodiment of the present invention;

FIG. 2 is a cross-section of the cutting insert shown in FIG. 1;

FIG. 3 is a laser apparatus used in a method of manufacturing a composite rod in one embodiment of the invention; and

FIG. 4 is a crusher used in a method of manufacturing a composite rod in one embodiment of the invention.

Detailed Description

The production of composite rods having cermet blocks of predetermined size and shape can be more cost-effective to implement by using recycled cermet, such as recycled WC. However, recycled WC is not common in the sizes typically used in composite rods, so it is necessary to break the recycled WC sheets into smaller pieces sized to fit the composite rods. This can be achieved by simply crushing the WC sheet and sieving the resulting crushed WC to separate the desired size of the mass. However, this approach has been found to result in significant waste.

Fig. 1 shows a cermet sheet, which is a used cutting blade 10 for a machining tool (not shown). The cutting insert 10 is a generally cubic piece of metal cutting grade WC that contains WC grains in a metal matrix material. The metal matrix material may be cobalt.

The insert 10 has a cylindrical hole 14 through the center of the largest face of the cube. In the embodiment shown, dimensions A and B are 19mm, dimension C is 6.35mm, and dimension R is 7.9 mm. The cutting blade 10 is therefore somewhat larger than the WC mass used in conventional composite rods, so the blade 10 needs to be broken into smaller masses before it can be used to manufacture composite rods.

Although a used tungsten carbide cutting blade is shown in FIG. 1, those skilled in the art will appreciate that the present invention is applicable to a variety of other cermet sheets, including titanium carbide or chromium carbide cutting blades, or sheets of tungsten carbide, titanium carbide, chromium carbide that are not cutting blades. These sheets may be virgin or recycled. The method of the present invention is also applicable to cermet cutting inserts or other cermet sheets in which superhard material is embedded. For example, the invention is applicable to a cermet sheet having a layer of Cubic Boron Nitride (CBN) or polycrystalline diamond (PCD) adhered to all or part of its surface. Such a sheet may be a new or recycled cutting insert having CBN or PCD at one or more corners of the cutting surface of the insert.

It should be understood that the dimensions given above, and even throughout the specification, are non-limiting examples. It should also be understood that essentially any shape of cermet sheet may be used as part of the method of the present invention; the cutting blade 10 shown in fig. 1 is merely one common shape of cutting blade, and those skilled in the art will appreciate that various other shapes are also useful. Furthermore, the presence of the cylindrical hole 14 is not essential to the invention. The hole is used to secure a drill bit (bit) to the tool body when the cutting blade 10 is first used. Typically, one of the corners actually forms the cutting edge of the drill, and the drill is able to rotate to react different corners as it wears.

In one embodiment of the present invention, cutting blade 10 may be scored along lines 16A-16D by the application of a laser. For example, a diode laser having a power output of 1 to 3kW and a spot width of 0.1mm to 0.6mm may be passed along the lines 16A-D at a speed of 10 to 30 mm/s. Preferably, the power of the laser is between 1.9 and 2.5kW and the speed is between 15 and 25 mm/s.

In another embodiment, cutting blade 10 may be formed by applying CO along lines A-D₂A laser to score. CO 2₂The laser may have a power between 1kW and 2kW and may pass through a spot width of approximately 0.4mm at a speed between 10mm/s and 20mm/s along lines 16A-D. Those skilled in the art will appreciate that other lasers, such as solid state crystal lasers including neodymium lasers and ytterbium lasers, may also be used to score the cermet sheet.

The application of the laser causes local melting and vaporization of the material in the region around the lines 16A-D. This results in a small amount of material being removed along the lines 16A-D, which locally reduces the strength of the cutting blade 10 and creates a cut where cracks may be expected to initiate when the cutting blade 10 is stressed.

In another embodiment, the score along lines 16A-D may be formed using other known cutting techniques, such as spark erosion, wire cutting, or trimming.

Fig. 2 shows a cross-section of cutting blade 10 along line D-D after the laser is applied along line 16A. As shown in fig. 2, there is a cut 19 along line 16A due to vaporization of the material when the laser is applied. It should be understood that the cuts 19 may be formed using alternative cutting techniques such as spark erosion, plasma cutting, wire cutting or trimming, and the like.

Advantageously, the use of a laser to form the cut 19 may also result in the initiation of a crack 20 by the cutting blade 10. Without wishing to be bound by any particular theory, applicants believe that the application of the laser causes local heating of the solid material surrounding the wires 16A-D. Fig. 2 shows an approximate temperature profile 18 across the cross-section along the blade 10 shortly after the laser is applied along line 16A. Fig. 2 shows the profiles 18 relatively close together in the region closest to the cut 19, which indicates a high temperature gradient, and the profiles 18 become progressively further apart as the distance from the cut 19 increases. The high temperature gradient causes stress in the blade 10 because the thermal expansion of the material is greater at the hotter regions of the blade (i.e., closest to line 16A) than in the cooler regions. As described above, the cut 19 locally weakens the cutting blade 10, thereby increasing the stress intensity caused by thermal expansion of the solid material around the cut 19.

Applicants believe that due to the brittleness of WC (and indeed other cermets), stresses caused by thermal expansion and local weakening typically cause the crack 20 to propagate at least part way through the insert 10. If the crack propagates all the way through the blade 10 (as shown in FIG. 2), the blade breaks along line 16A. Alternatively, the blade 10 may not break if the crack propagates only part of the way through the blade 10. However, the blade will already be significantly weakened along line 16A, and therefore the stress required to break the blade will be significantly reduced.

The cuts 19 extending along the length of line 16A are localized stress lines on the surface of the cutting blade 10. Within the scope of the present invention, a local stress line is considered as a line along which the stress in the cermet sheet will increase locally when the cermet sheet is subjected to an external force (compared to the stress expected in the absence of the stress increase line). However, it should be understood that it is not always necessary to apply an external force to the cutting blade to break it in practice. For example, the application of laser light alone may be sufficient to destroy the cermet sheet.

Fig. 3 shows a schematic view of a laser device 30. The laser device 30 may be used to score a cutting blade 10 or other cermet sheet along a line intended to fracture the cermet sheet together. The laser device 30 includes a laser capable of providing a beam of suitable power, wavelength, and focal width to initiate cracking of the tungsten carbide cutting blade 10 or other cermet sheet. For example, the laser may be a diode laser or CO₂A laser having an output power of between 1 and 2kW and a spot width of between 0.1 and 0.6 mm.

The laser 36 is oriented so that it can direct a beam 37 at the table 32, the table 32 being movable in a plane perpendicular to the beam direction under the control of a computer 38 having a user interface that allows a user to pre-program the movement of the table. The computer is also operable to control the laser 36. To score the cutting blade 10 using the laser device 30, the operator loads a tray 34 having a plurality of cutting blades 10 and places the tray 34 on the table 32. The operator then sets the laser power and optionally other operating parameters of laser 36 and the movement pattern of table 32 via the user interface of computer 38. The cutting blades 10 may be arranged on the tray 34 in a predetermined pattern such that the motion pattern selected by the user causes the laser beam 37 to score each cutting blade along the line along which it is desired to break, which in the embodiment shown is lines 16A-D. Once stage 32 completes the motion pattern, the laser is turned off (in fact, the duration of time that the laser is activated may be set to be the same as the length of time required for stage 32 to complete the motion pattern). The tray 34 may then be removed from the table 32. As described above, scoring the cutting blade 10 with the laser 36 may result in a crack starting from the kerf 19 that may propagate all the way through the cutting blade 10, causing the cutting blade to break. However, the crack may only propagate through a portion of the path of some of the cutting blades 10. Therefore, it may be necessary to apply an external force to the cutting blade 10 to break the unbroken blade or to perform a sieving or manual sorting operation to separate the broken blade from the unbroken blade. In fact, the sieving or manual sorting operation may be performed before the external force is applied, so that the external force is applied only to the unbroken cutting blades. However, in some embodiments, the number of cutting blades that remain unbroken after laser scoring is small enough so that it is more economical to remove the unbroken cutting blades for replacement recycling than to apply an external force to break them.

It is possible to randomly distribute the blades 10 in the tray 34. While this results in a random distribution of the shapes cut from the blade, they still have a relatively uniform overall shape because they still break along a line parallel to the laser application line 37 and the direction of movement of the tray 34.

As noted above, in some embodiments, scoring is not performed with a laser, but is performed by wire cutting, spark erosion, or trimming. In these embodiments, the score itself is less likely to cause the cutting blade 10 to break. Thus, if a laser is not used to score, it is generally necessary to apply an external force to substantially all of the cutting blades.

If external forces are applied to some or all of the cutting blades 10, they may be inserted into a wear plate crusher 40, shown schematically in fig. 4, via an inlet 41. The wear plate crusher 40 comprises a tapered first wear plate 44 and a stationary female wear plate 42, the wear plate 44 rotating about an axis 46. A small annular gap 43 is defined between the lower end of the concave wear plate 42 and the conical wear plate 44, which gap provides an outlet from the wear plate crusher 40. It may be that the vertical distance between the concave wear plate 42 and the conical wear plate 44 is adjustable so that the size of the annular gap 43 is adjustable.

When the cutting blade 10 is inserted into a wear plate crusher to rotate a tapered wear plate, various mechanical forces are experienced due to the impact on the

wear plates

42, 44 and the shearing action between the

wear plates

42, 44. Because the scoring of the cutting blades results in localized stress lines, the mechanical force exerted in the breaker 40 is significantly more likely to break the cutting blades along a plane passing through lines 16A-D than along other planes. Thus, scoring and applying external forces to the cutting blade results in a more predictable failure of the cutting blade. This facilitates the production of cermet blocks of predetermined size and shape.

It should be appreciated that the wear plate crusher 40 shown in fig. 4 is merely one example of an apparatus that may be used to apply a force to completely break the cutting blade 10 once scored. For example, the cutting blade may be broken in a mechanical press or a hydraulic press, or the operator may manually break the split cutting blade. The process for applying the external force to break the cutting blades after scoring will depend on the method by which they are scored. For example, the external force required to break a cutting blade that is scored by wire cutting may be greater than the external force required to break a cutting blade that is scored by laser because the application of a laser typically causes a crack to propagate at least part way through the cutting blade, thereby weakening it.

In another embodiment, a second laser may be provided in addition to the first laser, the first laser having a power and wavelength suitable for scoring the cermet plate, the second laser having a larger spot size than the first laser. The second laser is configured to generate additional thermal stress in the region around the kerf generated by the first laser, thereby causing the crack to propagate further through the cermet plate. The first laser and the second laser are preferably applied simultaneously, but they may also be applied sequentially. Advantageously, this embodiment may increase the likelihood that the application of laser light alone may cause damage to the cermet sheet. Other methods of inducing thermal stress in the cermet sheet after it has been laser scored may also be used to promote crack propagation. Such an approach may avoid the need to apply external forces. A system similar to that shown in fig. 3, but with an additional laser (not shown) may be provided for use in conjunction with the present embodiment.

Once the cutting blades 10, or indeed any other cermet pieces, have been broken into a cermet block of the appropriate size for use in a composite rod, they may be combined with a brazing material to form a composite rod. This may be performed by various methods that will be well known to those skilled in the art. For example, the cermet block can be washed, placed in a rod mold and heated to a predetermined temperature. Alternatively, the molten flux may then be poured into a mold. The brazing material, for example, in powder form, may then be placed in a mold, and the mold, cermet block, and brazing material may be heated to a temperature high enough to melt the brazing material, thereby causing the brazing material to flow around and coat the cermet block. Once the brazing material cools and solidifies, a composite rod is formed. It should be understood that the mold may be made of graphite or other suitable material that facilitates removal of the composite rod from the mold. From US3304604, US2137471 and US1977128 there are known methods for manufacturing composite rods from blocks of hard material, such as cermet and brazing material.

Depending on the nature of the cermet sheet and the resulting cermet block, it may be necessary to clean the cermet block before it is used to form the composite rod. Furthermore, it is often the case that the cutting blades are provided with a coating which reduces their wettability by the brazing material. Thus, if cutting blades are used as the cermet pieces, it may be necessary to remove the coating before the cutting blades break into cermet pieces or before the cermet pieces are combined with the brazing material to make the composite rod. The coating may be removed by chemical or mechanical means. As will be appreciated by those skilled in the art, the precise method for removing the coating will depend on the particular type of coating that has been applied to the cutting blade.

In another embodiment, the cermet block may be brazed to the tool without first being combined with a braze material to form a composite rod. For example, the cermet block may be spot welded to the surface of the tool to be hardfaced to provide a weak adhesion between the surface and the cermet block, and a brazing material may then be applied to fill the gaps between the cermet blocks and to firmly adhere the cermet block to the surface of the tool.

A particular advantage of the present invention is that it provides a method of producing pre-sized cermet blocks from used cermet plates (e.g., used cutting blades) without waste caused by simply crushing the cermet plates and discarding blocks of undesired size. Thus, composite rods having excellent wear and abrasion properties can be produced at relatively low cost.

Example 1

Applicants have used laser scoring to break up used bonded WC cutting inserts made of cobalt bonded tungsten carbide and small amounts of titanium carbide and tantalum carbide. The cutting insert is rhombohedral in shape with two rhombohedral shaped faces with corner angles of 100 and 80 degrees and a rhombohedral side length of 16mm, and four rectangular faces of 16mm x 6.35mm perpendicular to the rhombohedral shaped faces. The insert had a cylindrical hole 6.35mm in diameter through the center of the rhombohedra. The blade breaks along two planes, each plane passing through the center of the rhombus and perpendicular to a pair of edges of the rhombus.

Using Trumpf Trudisk Yb: the YAG thin disk laser scores one axis on each plane along which the cutting blade is to be made. The laser was set to a power output of 2kW and a laser spot size of 0.6mm and moved at 20mm/sec relative to the cutting blade. Scoring was performed in pure argon cutting gas.

Scoring alone results in more than 80% of the inserts breaking along two planes, resulting in WC blocks ready to be combined with the braze material to produce a composite rod. The uncrushed insert is broken along the axis by applying an external force with a hydraulic press and then broken along a plane to produce a block of the desired size. It has been observed that relatively low stresses (compared to the stresses required without scoring) are required to break the cutting blade that did not break during scoring.

The cermet block is combined with a brazing material to produce a composite rod.

Within the scope of the present application, "cermet" is considered to be a material comprising a ceramic, such as tungsten carbide or titanium carbide, embedded in a metal, for example cobalt. It should be understood that this cermet is referred to throughout the application by the name of existing ceramics, without any indication of which metal it embeds.

Throughout the description and claims of this specification, the words "comprise" and "comprise", and variations of the words "comprise" and "comprising", mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not limited to the details of any of the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the methods or processes so disclosed.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

1. A method of manufacturing a composite rod from a brazing material and a sheet comprising a cermet, the method comprising:

scoring a surface of the sheet by means of laser generated thermal stress to create at least one local stress line;

combining a cermet block with a brazing material to produce a composite rod;

wherein the cermet is a material comprising a ceramic embedded in a metal.

2. The method of claim 1, wherein the act of scoring the surface causes at least a portion of the sheet to crack and eventually break without the application of further external force.

3. A method according to claim 1 or 2, wherein at least a portion of the sheet is broken along local stress lines by applying an external force.

4. A method according to claim 3, wherein the external force comprises the action of a mechanical crusher or press.

5. The method of claim 1, wherein the cermet comprises tungsten carbide.

6. The method of claim 1, wherein the cermet comprises titanium carbide.

7. The method of claim 1, wherein the cermet-containing material further comprises a superhard material on the cermet surface.

8. A method according to claim 7, wherein the super-hard material comprises polycrystalline diamond (PCD) or Cubic Boron Nitride (CBN).

9. The method of claim 1 wherein the scoring of the sheet is accomplished by a first laser.

10. The method of claim 9, wherein the first laser comprises CO₂A laser.

11. The method of claim 9, wherein the first laser comprises a diode laser.

12. The method of any of claims 9-11, wherein the thermal stress is generated at least in part by a second laser different from the first laser.

13. The method of any of claims 9-11, wherein the first laser has a power of 1kW to 3 kW.

14. The method of any of claims 9-11 wherein the scoring is performed at a speed of 10 to 30 mm/s.

15. The method of any of claims 9-11, wherein the laser has a spot width of 0.1mm to 0.6 mm.

16. A method according to any of claims 9-11, wherein scoring the sheet is performed by loading the sheet onto a table of a laser device, directing a laser onto the table, and moving the table relative to the laser.

17. The method of claim 1 or 2, wherein the sheet comprises a used machined tool tip.

18. A composite rod made according to the method of any preceding claim, wherein the composite rod comprises a cermet block having a score line along at least one edge thereof, wherein the cermet is a material comprising a ceramic embedded in a metal.

19. The composite rod of claim 18, wherein the score line comprises a residue of a laser score line.

20. A method of using a sheet comprising a cermet to hardface a surface to be hardfaced, the method comprising:

scoring a surface of the sheet by means of laser generated thermal stress to generate at least one local stress line;

brazing a cermet block to the surface to be hardfaced;

wherein the cermet is a material comprising a ceramic embedded in a metal.

21. The method of claim 20, wherein the cermet block is spot welded to the surface to be hardfaced prior to brazing the cermet block to the surface to be hardfaced.